How can I retake the ASVAB?

Step one- google the nearest military installation
step two- locate their education office
Step three- call them, or walk in and ask about retaking the ASVAB (its called something else for Service members but they will know what you mean)
Step four- let them give you a practice test as well as assign you a tutor (free)
Step five- meet with your tutor on a regular basis
Step six- actually retake the ASVAB

I would recommend that you first work with your Training and Ops NCOIC first.

I was in the USAR (AGR) when I retook my ASVAB. I recommend you purchase and ASVAB study book with pretests. Once you complete the pre-test you'll know your good areas and the bad areas.
Research the specific test subjects that combine & makeup the MOS you're considering.
Then all you have to do is study these subjects you scored the lowest on (because the subjects you did well on don't need any more studying).
When I came back from my second back to back tour in Iraq, in 2008, I was able to make an appointment at a National Guard facility for my ASVAB retake.
My original GT score was 97 (this was way back in 1995 when I was in high school).
My updated ASVAB score came out to 111!
Good luck!

To retake the ASVAB, here’s how it works:
1. Talk to your recruiter – They’ll schedule the retest for you.
2. Wait at least 30 days after your first test to retake it.
3. If you take it a third time, you must wait another 30 days.
4. After that, you must wait 6 months between each retest.
Read this post to know detail about the steps:
https://easy-prep.org/blog/how-many-times-can-you-take-the-asvab/