Hello Sir,
Before doing any repairs to cracks, it should be checked that the cracks are stabilized and are not widening any further.
a) Cracked joint should be enlarged and racked out with iron tool at least up to 25 MM depth.
b) All loose material should be cleaned and cracked portion must be kept moist at least 24 hours before the repair.
c) Cracked portions must be refilled with cement, coarse sand mortar 1:4. After that the cracked portion must be plastered with cement mortar 1:4.
d) Repaired surface should be kept moist up to 7 days and if adjoining bricks show cracks, these bricks should be replaced by new bricks.

For more detail click on the link below:

How to Repair Cracks

Thanks