Pray that God would circumcise their hearts.

Circumcision was the Old Testament sign of entering into God’s covenant, of being God’s people. To have a circumcised heart symbolizes having a heart that is fully joined to God, fully submissive to him.
Pray that God would give them a heart of flesh.

The Bible contrasts a heart of flesh, a heart that is alive and responsive to God, to a heart of stone, a heart that is cold and unyielding. Pray that God would work within these unbelievers to change their hearts.
Pray that God would put his Spirit within them.

The great joy of salvation is being indwelled by God himself. Pray that God would grant this honor to those unbelievers, that he would choose to take up residence within them.