There is a lower panel below the dash that needs to be removed.
98 blazer heater core removal.
Turning them counter clockwise will loosen them.
Go to passenger side of dash and remove glove box for working room.
Pretty easy to do.
Disconnect the heater hoses under hood.
Once panel under dash is removed you will see the heater box remove the 6 8 bolts around the very base of it it will able to be lowered down and you will see the heater core it has a couple of brackets that hold it in place remove these.
Remove the heater core access cover screws.
Squeeze the clamp and slide and twist the hose as you pull them off.
How to replace heater core on my 1998 chevy blazer.
Remove the heater core hoses on the upper left of the engine bay by pinching their hose clamps with a pair of pliers and pulling them off.
Remove the heater core intake and return hoses from the core nipple by releasing the squeeze clamps using channel lock pliers.
Remove mounting bolts holding the heater core cover in place using swivel sockets and extensions.
Disconnect all of the vacuum lines from the heater assembly.