All the league and tournament results on SquashLevels are imported automatically from the various source systems so the place to fix an incorrect result is on the source system itself. Once corrected, that result will be re-sent to SquashLevels during the nightly processing and all will be well.
Players can't update results that have been received from official sources though admins potentially can but there's no point as it will just be overwritten again at the next automated results pull.
You can edit informal club matches, box matches and friendlies if you are one of the players. To edit your result on SquashLevels, click on the match date in the player history and you will be taken to a page from which you can edit it. Note that; you must be logged on, you must be one of the players and the update will be recorded so we can track who is changing what.
You didn't play this match at all
This does happen from time to time when a match is entered with the wrong player - which could be you.
Sometimes it's just a simple mistake but other reasons might be that team captain was constrained to set of players (e.g. by membership or league rules) in which case they possibly couldn't record the correct player on the system.
Whatever the reason, this is still a case of in incorrectly recorded match and, if formally entered on a source system then it needs to be corrected on that system first.