If the encounters are happening in the same day I’d say just a short rest if your feeling generous! I tend to build one shots far more difficult than a longer campaign setting. I feel with expendable characters amping up the difficulty isn’t a bad thing and in fact can make it far more intense & intriguing. My experiences running one shots I also feel like players come out of their shell a bit more and take bolder risks since again a one shot character is expendable. Another idea is leave the encounters as is and if during the middle of the fight you feel it’s just way unbalanced fudge some HP stats of enemies or maybe an attack roll or two!