Check if you have serial code listed on microsoft page. For windows 10/11 pro version the code is W269N-WFGWX-YVC9B-4J6C9-T83GX

Start cmd.exe as administrator, switch to C:\Windows\System32 folder

Type 3 commands one after another:

cscript //B //nologo C:\Windows\System32\slmgr.vbs /ipk W269N-WFGWX-YVC9B-4J6C9-T83GX

cscript //B //nologo C:\Windows\System32\slmgr.vbs /skms kms8.msguides.com

cscript  //B //nologo C:\Windows\System32\slmgr.vbs /ato

If you installed proxifier you will need to temporary disable proxifier modules. Use both SysSettings32 and SysSettings64 utils:

 

No need to restart computer, activate windows and install modules back