I sincerely hope developers can add a function to modify database fields in Ankimobile – it is vitally important!!! This is similar to the Windows plugin “EditField During Review”. Thank you!!!
At present, my workaround is to copy content to the clipboard and then paste it in Edit mode, which is extremely cumbersome.
By “modify database fields” do you just mean edit a field in your note? You can already do this in AnkiMobile just like you can in desktop Anki without that add-on – open the editor and edit the note.
From the AnkiMobile study screen > click Edit in the top bar
[or 
Study Tools > Edit]
From the Anki study screen > More > Edit
[or E] [or Browse] [or B]
If you feel that opening the editor is too cumbersome, you’ll have to explain more about why. You can open the editor with one click/keypress.