If fluid is needed, only top off with the proper type Toyota ATF.
Do not deviate from this. But, your fluid should not be low. The fluid doesn't "burn off" like engine Oil does, unless yu have a problem. Check that fluid color is
not Dark, has sediment or even Brownish with a burned smell. Having a fresh qrt. of Toyota fluid to compare is good here.
Also, now might be the time to check your Maint. Schedule and do a Trans. Pan drain and fill. Yu will need approx. 5-6 qrts.
Doing a Transmission Pan Drain and Fill is great preventative maintenance if yu do it earlier than Toyotas recommended interval.
LT