Hi I have a question regarding light metering for medium format and if I need to convert my lens like I would for cropping.

When shooting 35mm I light metered everything with a free app that's simply called light meter. I recently bought my first medium format camera (A Mamiya C330) that shoots 6x6 format Now I use the website omnicalculator to calculate the lens equivalent regarding focal length and depth of field (f stop) and my question is does this equivalent also apply to measuring with the light meter app? Do I tell the app that I am shooting on the (55mm) with f4.5 like it says on the lens, or do I tell it the 35mm equivalent lense of (30mm) f 2.5?

Pls help me not ruin my first roll of 125 Film by under/overexposing it :D