Combined Excise Tax Return In Washington State

My husband is self-employed as a Remodel Contractor. He collected tax from his customers.  The customers sent him a 1099-NEC. The total income (Box 1) includes the tax he collected. He paid that tax collected back to the State (by filing the Combined Excise Tax Return).

Question: Where do we enter this tax payment he paid to the State? We don't think the tax he collected is actually his income because he sent it to back to the local/state already. So where on the 1040 tax form do we need to offsite this amount? Any suggestions? Thank you!