auxiliary N4 common casualpolitewritten
〜であげる — voiced allomorph of 〜てあげる
〜であげる ・ であげる
Builds on て形
A full written guide for 〜であげる is on the way.
This point is mapped in the grammar tree, but its examples, formation table and usage notes haven't been written yet. The fastest way to learn it now is to meet it in real sentences inside Jengo.
See 〜であげる in real sentences
Jengo shows 〜であげる the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Basic Japanese Grammar. Editorial confidence: medium.