Hi,
ifixit does not do repairs to equipment.
We are all volunteers who will advise you on what you need to do to fix the problem yourself.
Here is a link to the ifixit [guide|31667] guide. This will help you to gain access to the motherboard in your laptop so that you can remove / replace the audio (combo headphone/mic) jack.
You will need SMD soldering expertise and tools to effect the replacement.
Here is a link to just one [https://www.aliexpress.com/item/5pcs-lot-Headphone-MIC-Audio-Jack-Connector-for-Dell-Inspiron-3521-motherboard-etc-Earphone-Cobo-ports/32612226370.html|supplier] of the replacement part. It is a very hard part to find for your model as most places are out of stock. This is the best that I could manage. You may have more luck in finding a supplier that suits you better. Just search for ''Headphone MIC Audio Jack Socket Connector for Dell Inspiron 15R 3521''
If you find that doing the repair is too daunting, then I suggest that you contact a reputable, professional laptop repair service and ask for a quote to repair the laptop.
Hopefully this is of some help.