preincubate

transitive verb

pre·​in·​cu·​bate -ˈiŋ-kyə-ˌbāt, -ˈin- 

preincubated; preincubating

: to incubate (as a cell or a culture) prior to a treatment or process

red cells were preincubated with cholinergic ligands

—D. P. Richman et al.