For each entry in Schedule C, use Ctrl + E to allocate that income/expense/depreciation item etc. What states are you working with. What is the resident state. Some don't really care where the income came from, they tax it anyway. The net affect is how the credit for taxes paid other states shows up. 

State receipts: AL, GA, IL, IN, KY, MS, MO, SC, TN, TX, VA, WV, WI

Resident state with Assets & Rent: OH

Any payroll?

Are you sure you have to file in all those states? What gives them nexus?

Payroll in three states plus resident state. May not have to file in all of them.

First, read the instructions for each state to see what constitutes nexus for filing requirement. This may lead you to state law.

After you determine where you need to file, set up each state in Lacerte and make sure to enter the nonresident info for each state. Make sure Ohio is listed as resident state.

Okay, I do need to check for nexus but I've done the rest. It still looks like the schedule C details have to be allocated to each state manually.

Yes, but you can cheat a bit. Suppose you have one big deduction for Office Supplies > You can do all of your allocation there. You are really only concerned that the net of Schedule C be accurate for each state, not necessarily that each income and expense item matches. You might be able to  get the proper net just by tweaking the Gross Income. 

✔️Help Article How to allocate amounts on a multi-state 1040