"Pima afya yako"
Translation:Check your health
The direct imperative without an object prefix is simply the verb stem with the ending unchanged, so, in this case, pima.
If you add an object prefix, then you need to change a final "a" to "e", for example ipime "check it".
The "e" ending is also used for the subjunctive, which always has a subject prefix.
Upime = You should check.
Uipime = You should check it.
Usipime = You shouldn't check / Don't check.
Usiipime = You shouldn't check it / Don't check it.