Any guide on how to do this? I use 3600 with b450 Tomahawk Max but left it at default because I have zero experience on overclocking.
Sorry I don't have a guide personally. I'm waiting on new GPUs and so I'm GPU bound all the time anyways so I've not bothered.
I've read a lot about it, but it is a bit different on different motherboards.
Just generally you want to download Ryzen Master, make a new profile and set it to Auto-Overclock and on the top left pick +100 or more mhz. Apply and restart then enter the BIOS and enable PBO (Precision Boost Overdrive) and set it to either enabled, enhanced or if you want to get detailed with it manual. This is raising the power limits, which is safe because the CPU wont ask for more voltage than it can handle, these settings just make sure the CPU is deciding how much power to take instead of an arbitrary limit.
It should be beneficial at this point to set a core voltage offset of -0.0500 to -0.0750 because the CPU tends to take more voltage than it actually needs.
Make sure to benchmark the CPU before and after so you know if your practical performance actually improves. Too low of a voltage offset will still show higher frequencies but performance will be lower because of clock stretching.
As I've said, not done it myself but there should be zero risk to doing this. Still, you are mucking around in a BIOS and clicking past warning notifications and so don't do it if you don't feel confident.
At the end of the day the performance increase is quite minor, the 3600x is basically never a recommended purchase because the higher frequency doesn't improve performance all that much.
Edit: Consider looking to DRAM calculator for Ryzen since overclocking RAM actually has a big impact on performance. You give it your RAM details and it spits out some likely safe overclock settings, you can take those settings and put them manually into your BIOS.
If I'm going from Intel to AMD, do I need to reset windows etc?
Can't hurt, but no definitely not necessary.