https://www.allaboutcircuits.com/projects/flashing-the-ESP-01-firmware-to-SDK-v2.0.0-is-easier-now/
Incase you have issues I should say I did not follow the page from the start. I made several other attempts. And after some initial progress ended up flashing the ESP with the instructions on the page above. My exact steps were as follows.
1. Download Nodemcu-flasher from https://github.com/nodemcu/nodemcu-flasher
2. Place ESP in flash mode by wiring GPIO0 to ground. (it would not work at first when I tried to use a pull down button I had in place on my breadboard)
3. Set the Nodemcu-flasher settings to the one attached in the picture (Note that my board is and ESP-01. your setting may be different)
4. Nodemcu-flasher worked to remove the blink sketch, but was stuck in a restart loop.
5. repeated Step 2 again.
6. Now flashed the ESP-01 using the files and setting from the above webpage (same as the attached picture)
ESP8266 ESP-01 acting like new again. AT+ Commands working and able to connect to my local wifi. .
Hope this helps if you're still having trouble.