Going to Lake Como in Oct. for 4 days. We need to know what we should do while there. Thank you

Don’t know about ‘should ’, but you could have a great time riding the ferries around to the various towns, and getting off and exploring. Here’s the ferry website: https://lakecomotravel.com/boat-tours-ferry-lake-como/

Not what you should do but what you like to do. First, visit the local tourist office and pick up some local guides. You are on a large lake so take boat rides to visit some of the other towns on the Lake. Check out walks in the area. There is a funicular that takes you up a mountain. Shop. Relax and enjoy the stunning scenery. Eat leisurely lunches and watch the world go by. Eat gelato. Swim in the lake. Go to a concert. Relax some more. There are museums and art galleries, parks and gardens to visit. Relax and enjoy the views.

Been to the lake but not the town of Como. First day I'd explore Como and otherwise get my bearings. The next day I take the ferry to a few other towns that intrigue me. On the third day I might relax in the morning and then decide to either dig deeper into Como, maybe cross the Swiss border, and/or get back on the ferry. The last day I'd relax some more and revisit a couple of my favorite waterholes discovered in the previous 3 days.

...would like to know what we should do each day

You must have had at least one reason why you chose this place to visit. We don't know what that reason was. We don't know what your interests are. Go online to explore the tourist information sites that deal with Lake Como and see what piques your interest and do that.