Toilet gasket not holding water. Need a temporary fix.

Turn off water supply
Open toilet ball/blade
Using your hands clean the seal thoroughly top/bottom/sides flexing it as you clean (straight dishsoap)
Rinse seal clean
Dry with paper towels
Using your hands coat seal thoroughly with olive oil really working it in

IF seal will not hold water at that then it is torn/ripped/gouged or ball/blade has gouge

Replacement then is only fix. Sometimes a new toilet is easier.

New Dometic 300 Series.....seal can be replaced w/o disassembling toilet
Just pops out and back in thru bowl.