I'm not an android user but was fairly certain I saw some notes that the default amount can be edited in the settings, have a look.
It could be Damus though, I've been reading a lot on Nostr the last few days since Zap-endance Day occurred.
Discussion
On notes, in Amethyst, they're set to 1k, but using Snort, you can set your own. There's setting for a default amount in getalby, but it has limited propagation across clients, in my experience.