'Do' and 'does' are the two forms of the present indefinite tense in the verb 'to complete.' Which a single you can use will mostly rely on the sentence's topic. Their utilization is nearly equivalent, except for one particular occasion where You need to use 'do' instead of 'does.' https://financefeeds.com/senate-passes-genius-act-bringing-us-stablecoin-rules-closer-to-reality/