Heater not working?

There is a loose connection or a bad ground somewhere. I am giving you the wiring diagrams for the heater circuit and the radio circuit. Look to see if they share a common ground. Check the ground, there location is given at the ground sign, and make sure it is a tight fit, corrosion free with a good metal to metal contact. Wiggle wire connectors around while running, careful not to grab to close to actual connectors to avoid shock and where rubber gloves, to see if there is a loose wire.

This guide can help us fix it

https://www.2carpros.com/articles/car-heater-not-working

Please run down this guide and report back.

Does the engine reach normal operating temp? Are the heater hoses hot? Possible thermostat issue? Maybe a temp control door under the dash, isn't operating like it should?

Yup, not enough coolant flowing thru the system-the heater core is on a higher level then the radiator. A stuck open thermostat will also do that, also a clogged up hose and heater core.

Check power supply
place switch on high
with a test light check the blower motor wires
one should have power and the other should be ground

Check coolant level
Is the car reaching operating temp
Check heater core hoses if both are hot,
if both hoses hot and not enough heat inside suspect blend door actuator
if not one hose hot and the other warm or cold the heater core need to be flushed (very common)
as a 1st step
these are the steps
WARNING: NEVER REMOVE THE PRESSURE RELIEF CAP UNDER ANY CONDITIONS WHILE THE ENGINE IS OPERATING. FAILURE TO FOLLOW THESE INSTRUCTIONS COULD RESULT IN DAMAGE TO THE COOLING SYSTEM OR ENGINE AND/OR PERSONAL INJURY. TO AVOID HAVING SCALDING HOT COOLANT OR STEAM BLOW OUT OF THE COOLING SYSTEM OR DEGAS BOTTLE, USE EXTREME CARE WHEN REMOVING THE PRESSURE RELIEF CAP FROM A HOT COOLING SYSTEM OR DEGAS BOTTLE. WAIT UNTIL THE ENGINE HAS COOLED, THEN WRAP A THICK CLOTH AROUND THE PRESSURE RELIEF CAP AND TURN IT SLOWLY UNTIL PRESSURE BEGINS TO RELEASE. STEP BACK WHILE THE PRESSURE IS RELEASED FROM THE COOLING SYSTEM. WHEN CERTAIN ALL PRESSURE HAS BEEN RELEASED, PRESS DOWN ON THE PRESSURE CAP (STILL WITH A CLOTH), TURN AND REMOVE PRESSURE RELIEF CAP.
Engine cool
lower the coolant level
Locate the two hoses running to the heater core
disconnect them at the engine side leaving hoses connected to heater core throw the firewall
use garden water hose and compressed air if possible
run the water and follow by air throw one side and out the other and vice versa
do that two to three times watching what leaving the heater core you are looking for the good flow and clear water to run throw
reconnect hoses
top off coolant system
good luck
let me know