You stay on TRT. You use hCG or Nolvadex to recover your testes.
You could use either or a sequence. For a sequence you would start on hCG to recover size and firmness of your testes then switch to Nolvadex to allow your pituitary to produce FSH which can improve sperm count and quality. As for how long all of that takes, some suggest longer to get a fresh batch of viable sperm. If you are older, quality sperm is an issue as there are associations with developmental defects thought to be related to age of males [sperm quality].
Your LH/FSH levels from Nolvadex are a crap shoot. You can do lab work after a while to see. You do not want high Nolvadex doses as T-->E2 conversion rates inside the testes can be very high and libido can suffer. Same if hCG dose is too high. Combining hCG and Nolvadex is then a problem as too much LH hCG creates problems. So do not combine.
We have seem some here trying to do the same thing, mapping out a long game plan then conception happens quick and game changes. So you might want to avoid pregnancy to improve sperm quality. There is more at stake than just getting pregnant. You can also get sperm analysis before you pull the trigger.
In many cases, 250iu hCG EOD or 10mg nolvadex EOD is adequate. You could try more for a couple of week to start, but longer risks some adverse effects.
If your hypothalamus and pituitary are in the game, you could use only Nolvadex. If you had deep secondary hypogonadism, the desired effect might be limited. With Nolvadex only, if you see the testes are recovering size and firmness, you know that things are working OK. If not, you can try hCG. LH/FSH lab work would be valuable, but often this is not done. Often with T hCG, men are fertile. Recovery from T only is an unknown and you can only see what happens.