There are numerious ways to value a business. During pre-revenue it's about feelings and things. Once revenue and actual trajectory.
Book Value
DCF -- Discounted Cash Flow
Profit Based
Using Profits
EBIDTA
Earnings Before Interest, Depreciation, Taxes and Amortization
Earnings
Revenue
409A
Paying a company to look at your revenues and growth and operations. Then you can figure it out.