What does "flash my controller" mean?  Thanks.

I recently purchased my first e-bike. I bought a pre-owned (originally bought in 2022) RadRunner Plus - cargo utility e-bike. It is rated to 500 Watts, 7 peddle gears, 5 Peddle Assist levels, with a half-twist throttle. It's heavy, 77 lbs with the battery. I just got the bike back from its break-in period inspection. So far I'd say it's a very comfortable ride with the 3.3 inch tires (semi-fat) and front fork suspension ...plus I replaced the original seat with an actual comfortable seat

About the inspection, the technician identified that the front wheel wasn't in the forks straight and as consequence the break pad was rubbing.  Now that the wheel is turning freely I've found the bike is much easier to peddle on my own.  A huge difference, I couldn't believe it!

Looking forward to getting to know this e-bike and the trails ahead.