If the percentage will not change, then click on the cost basis line and show your calculation for the 85% business on the supporting statement. If the business use changes such as a vehicle then my method won't work.

What type of asset? 

Computer

For the depreciation input, you have the option to enter the business percentage in the designated field. Alternatively, you can enter the final result directly and document the calculation in the software (which the client cannot access), or in another location that can be shared with the client.

Depreciation > Enter your asset, etc > Details > Auto & Additional Info > click Listed property > Scroll Down to Additional Information > Percentage of business use (.xxxx)