Tax adjustment on additional earnings from online teaching

Hello all,
I work as an English teacher for a medium size company. Over the last few months I have started doing extra lessons on an online language teaching platform as a way to supplement my income for my family (inflation killing me!).
I have a permanent resident visa, but my company doesn't allow secondary work in the same field. The amount of income from these online lessons is starting to balloon so I should declare them as additional income – I heard this is done in February. This may also get me deductions on my Internet bill, electricity, mortgage etc. If I do so, will it come back to my company?
Also what is the procedure for filing additional income? What forms do I need to fill out and where?
Thank you!

by ForeignPack4557