Is there any tool I could use to remove the iCloud activation lock?

iCloud locks are very difficult to fix, and sometimes impossible. If you can, contact the seller and ask them to remove the lock from the phone. Using iCloud or Find My iPhone. If you can’t, you are mostly out of luck. You may be able to use some tools online to remove it. But use them at your own risk.

*Answering due to low quality prior answers*

The iCloud lock is based on the device S/N, so there is no fix. You need to regain access to the Apple ID, or you need to have the receipt from when you bought the device to get it removed.

Unless you can do either of those things, it’s going to need a board swap - at which point, the phone is not worth fixing. Especially in 2022 as I answer this, as carriers blocked new activations of 3G phones years ago, and 3G is dying in 2022-2023 with the big 3*.
*T-Mo is shooting for a 2022 date for the EVDO/3G Sprint networks, but if Dish gets their way by continuing to cry, it may go out to 2023.

I am sorry to say no. there is no way bypassing iCloud lock, once it’s locked you have a brick.