to warn him
We must warn him.
She must warn him.
I need to warn him.
We tried to warn him.
We need to warn him.
Ей следовало его предупредить.
She should have warned him.
Она пыталась его предупредить.
She tried to warn him.
You have to warn him.
Мне надо будет его предупредить.
I’ll need to warn him.
I wanted to warn him.