I cant change avg swimming pace to meters/min, it remains yard/min. Units in app and phone are meters. Garmin 5x plus.
Ah, I just saw you meant Open Water Swimming so the pool size is irrelevant anyway. In that case reverify, what units are set on your device. It must be wrong, if the pace is shown in yards on the watch. You also did not tell what model you own, and where exactly you see the pace in yards - whether really on the watch, or rather in the GC Mobile phone app, or in Garmin Connect Web.
Try setting the language of your Android to English to verify the pace in yards is not just a translation problem. It definitely works all right for me, and I tested it in several languages, though I can't read hebrew, so cannot check that version.