yattajlpt.com/grammar/n5/te-ageru
Detailed guide to the て-form + あげる pattern for expressing doing something as a favour for someone, with explanations of politeness registers (さしあげる, あげる, やる), particle usage, and comparisons to related patterns like.
GrammarTe-formParticlesJLPT N5Tutors and teachersKeigo and politeness