A typo in entering the bid amount is the ONLY bidder error that may be corrected by retracting the bid. You must rebid the correct amount (the amount you intended to type in the first place) immediately after the retraction goes through. There are time limits (12 hours before the scheduled auction end or 1 hour after the bid was placed, whichever is later, but in no case later than the actual end of the auction) so don't delay if you actually made a typo.
https://www.ebay.com/bfl/retractbid
If you are simply regretting the amount you bid or made an error in calculating the amount or the like, you may not retract for that reason. You can message the seller and request that s/he cancel your bid but s/he is nor required to do so nor to respond to your message. S/he cannot give you permission to retract ("Seller said I could" is not one of the two valid reasons).
