Slitherine

I dont know how the pioners or enginers can clear a minefield
please help me

You have to get your engineers next to the minefield or tank trap or to a river. Then at the next turn, if you right click you will see the available actions. Some actions take more than one turn to complete.

Not sure if this works for all scenarios/campaigns, but it does for those that have been designed for it, or for mods that have this feature.