The title is really two separate queries in one that, while linked, can be treated separately.
How can I avoid streaks with wipe-on polyurethane?
With any varnish of reduced sheen, i.e. not high gloss, the main recommendation is to ensure thorough mixing. The matting agent (often very fine silica particles) invariably settles to the bottom of the container and very thorough mixing — can't stress this enough — or shaking is needed to ensure it is distributed evenly through the liquid.
Note: normally you are specifically advised not to shake varnishes and various waterbased clear finishes but wiping varnish is an exception since the application method means no bubbles can survive in the applied coating1.
You may be able to fix this with a further application of the wiping varnish as you've indicated in the Comments you're going to try, but failing that all is not lost and that's covered in the other part of the title.
How can I fix streaks with wipe-on polyurethane?
Although this can be a little trickier with satin and matt varnishes than gloss, you can generally alter (and simultaneously even up) the sheen of varnishes by rubbing down in various ways, after they have had sufficient time to harden.
This isn't something you can expect to do the day after the final coat went on, possibly not even the end of the week. The people who do this professionally tend to err on the side of caution and wait 10 days to a couple of weeks, and sometimes longer2.
Rubbing down (abrasion)
The general process to lower the sheen is to introduce scratches in a controlled way. These days this is most often done by rubbing with steel wool, Scotch-Brite or similar, or by very fine sanding. Traditionally this was often done using ground pumice or 'rottenstone' (very finely ground limestone) which are still available today if you ever want to experiment with them.
This process can be done wet as often advised in books, with soapy water or 'light oil' (these days it's common to use mineral spirits, WD-40 or a light mineral oil), in the case of steel wool in particular lubricated with paste wax, or completely dry. Doing it wet you can imagine the importance of working on a well-hardened varnish to avoid issues.
I'm personally a fan of steel wool for this purpose although some consider it obsolete, and generally recommend Scotch-Brite/an equivalent. While I don't think they work as similarly as some claim there's no denying that the results can be impossible to tell apart, and since results are all that matter pick whichever appeals to you the most. If using steel wool I would recommend 0000 (four-ought). If using Scotch-Brite the white, although grey might work OK with a light touch.
If you want to try it with abrasive paper use nothing coarser than 400 grit (~P600), and you might want to finish with 600 (roughly P1000).
There's more to any version of this process than can easily be described here so I advise a little further research if you've never done anything like it before.
Wax
You do not need to wax afterwards; varnishes in good condition do not need to be waxed. However, you can also try this as a means to further unify the surface finish if whatever you tried from the above didn't give quite the result you wanted; but as ever with wax, bear in mind this will need to be maintained for the life of the piece3.
1 Many/most being burst during application (depending on the method chosen) and more (possibly all) are burst at the wiping-off stage. Additionally the very thin nature of the varnish means that any surviving ones can easily burst on their own — one of the standard pieces of advice to reduce bubbles in brush-applied finishes is to thin slightly to increase the chance that bubbles can rise to the surface rather than being trapped in the viscous film.
2 It might be surprising but this is not necessarily because they were taught this, often it's because they learned the hard way what happens if they try to rush it :-)
3 Rewax 1-2 times a year depending on the amount of use the desk sees. Prefer paste wax over any liquid wax. If you're at all interested you can easily make your own paste wax at home, basic directions given at the bottom of this previous Answer.
