taking sotalol post ablation afib surgery told to stop sotalol 3 month after ablation I stop last night now resting pulse is 90 usually 78 normal?

Probably. After stopping Sotalol, you can experience an increase in the RESTING heart rate (measured after 5 minutes of no exercise, sitting or preferably laying flat, in a darkened room with all lights/sounds off). Most heart rate measurements are not true "resting" heart rates, so an increase to 90 may have confounding factors. A change from 78 to 90 is not significant, then. (Worry if it jumps to 100+).
Beta blocker. Sotalol is in the Beta Blocker class and can cause slowing of the heart rate, therefore it would not be unusual for your heart rate to increase on stopping.