My Neighbour wants me to cut back this tree – Help!

Hi, I moved into my property last year and have spent the last year getting my back garden ready to relax in. I have been caring for my elderly neighbours front garden, mowing the lawn and pruning the hydrangeas, however, last week she asked if I could cut this tree back (a Lawson cypress according to PicThis app) as it’s gotten so big she is no longer receiving any morning day light and I have no clue what I am doing. This is a picture of the tree and the inside I can see what has been done before. Any advise on what tools I should use, where I should start and in general what I should do would be greatly appreciated. Thank you!

Previous work was done by the guy who owned the property before me.