Odds are that you have a break in the heating elements and they are no longer generating any heat for you. Think of the heating threads in a toaster and that is a small version of your dryer. You will need to remove the elements and replace them with a new set. Not sure on your model where they are located. most likely there is an access panel in the back of the machine. Unplug the dryer, remove the access cover and remove the heating elements. there will be a couple of wires that connect to the heating element which need to be taken loose (Note where they are located) look over the element and if you dont see a break you can use an Ohmeter to check the terminals for continuity. One set will have two heating element wires connected to it and the others will be single contacts. Low heat uses one element and high heat uses two elements. Replace the broken set and reinstall and you will likely have solved your heating loss issue. Good luck.

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Replacement parts for WHIRLPOOL RES7646KQ3 29"ELECTRIC DRYER | AppliancePartsPros.com

See the attachment for the wiring diagram

Looking at the wiring diagram the unit shows a single heating element.

First check the power for 240 volts. Instead of messing with a live dryer, on this unit it can be checked by placing it mid-scale in timed dry. If the timer advances then you have 240 volts as the timer motor and the heater use this.

If the voltage is OK.
Open the unit up and check the heating coil (Item 17 in Section 3), they are usually around 10 to 12 ohms.

Note: When checking any part for resistance always disconnect one side of it. This prevents reading an alternate/parallel circuit path.

If heater is OK, check the thermal cut-off (Item 9 in Section 3), should be 0 ohms.
If open you have to find out what caused it to blow.
Check the heating coil.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 10 to 12 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case. This can cause it to run on high and the thermostats cannot regulate it so the thermal cut-off blows.

The hi-limit should have regulated the temperature so the fuse did not blow, that is why there is a new one with the thermal cut-off..
Note: That unless there is another problem in the unit the hi-limit should never have to open. It is just a safety device with the fuse being a backup safety device.

Just in case it is not a grounded element.
With all the below the high limit will also have to be replaced.
Check that the belt is OK.
Check the seals (drum etc) in the unit. The air is pulled over the heating coils, through the drum and pushed out the exhaust. So any large seal leak will pull in room air and the cycling thermostat on the blower will run the unit hot.
Check that the lint filter is not coated with fabric softener residue which greatly reduces air flow.
Check/clean your vent system.
Check/clean the blower wheel.

If all OK you may want to replace the cycling thermostat as it's contacts may not be opening (welded shut).

If thermal cut-off is OK check the hi-limit (Item 5 in Section 3) and the cycling thermostat (Item 8 in Section 3).
Note: The cycling thermostat has 4 connectors. Two are the contacts they should read 0 ohms. The other two are an internal heater, usually 5,000 to 10,000 ohms.