My doctor has diagnosed me with many seborrheic keratoses on my chest and back. Is there a home remedy or OTC product that I can use to remove these?

Barnacles . If these are benign seb ks, no need to do anything. Occasionally they will flake off. Some wart removers and freeze off solutions work. Be sure if these get removed, you know what they are. If you remove a dysplastic mole or lesion you may miss a skin cancer. I would check again with your physician before self treatment.
No. To remove these you need to go to right depth. Too superficial and they will return. Too deep and it will leave redness or even scarring. Curettage , scraping is an option, however , you need to have a section of about 10 done at a time. This unfortunately is cosmetic and will not be covered by insurance.
Seborrheic keratosis. Research conducted at the yamaguchi school of medicine in japan found that supplementing with vitamin d3 might help sebhorreic keratoses. About two weeks into the treatment, smaller lesions began to crust and fall off. Talk to your doctor before supplementing with vitamin d, as it is a fat-soluble vitamin; excess supplementation with fat-soluble vitamins in particular can lead to excess levels.