I have no idea what you have done to your Micro SD card, but before tell it is DEAD, I suggest you insert this SD card into your PC to test if it can be detected, if it shows RAW, and if it needs formatting. If so, things aren't all that bad. All you need to do is perform RAW SD card recovery and SD card formatting for future use.
In general, if an SD card is not formatting, editing, or showing up on your phone, the very first step is to check its file system. You can insert it into your computer and then head to Disk Management to have an SD card state check.
If the state reads RAW, then you should execute RAW SD card data recovery first. iBoysoft Data Recovery Software is highly rated for its excellence in data recovery, especially in RAW SD card data recovery. It contains three recovery modes: Data Recovery mode, RAW Drive Recovery mode, and BitLocker Recovery mode. With an intuitive and user-friendly interface, it is not tough stuff to restore data from your Micro SD card:
Step 1: Free download and install iBoysoft Data Recovery Software on your computer.
Step 2: Insert your Micro SD card and launch iBoysoft Data Recovery Software.
Step 3: Choose the Data Recovery mode and select your SD card from the list.
Step 4: Click Deep Scan and click Next to start the drive scanning until the process ends.
Step 5: Right-click the files to select Preview to check if your files and intact.
Step 6: Click Recover to restore your files and documents. Do not save the recovery results to the same SD card because you might suffer from data loss again.
After the data recovery, you can learn how to format your SD card on Windows here:
Step 1: Right-click "My Computer" (or "This Computer") on the desktop, and click the Manage option.
Step 2: Choose Disk Management and select your SD card and right-click it.
Step 3: Select Format... and choose a file system on the pop-up Format window.
Step 4: Check Perform a quick format and click OK, and then wait for the SD card to be formatted. Then you will have a Micro SD card with a new file system.
However, if this SD card can not be detected by your PC or any other device, I must tell you that it is dead. For your later storage work, you'd better utilize a new Micro SD card.
Hope you good luck!