There are some Windy layers which cannot be changed when using an Android or iOS device. Rain Accumulation is one of them. If you would like the list of layers which cannot be changed, it is available at Overview of units used on Windy. If you aren't interested in looking up items like this (as most users would not want to do also), then make any of those changes using the Windy website using a browser. Changes made using a browser save to the cloud and will then be available when using either an Android or iOS app. If you cannot make a change using a browser, then submit a bug report.