This solution is for Mac:
Considering you have already downloaded SDK platform tools & trying to set adb path:
If you want to check the SDK is available or not, just check it by following this path:
User > Library (Hidden folder) > Android > sdk > platform-tools > adb

To set the PATH for the adb command on a macOS system, firstly need to edit your shell configuration file. The default shell on macOS is Bash or Zash.
If you're using Bash, so you will need to edit the ~/.bash_profile file otherwise edit ~/.zprofile in your home directory.
Here's how to do it:
By Terminal:
- Open a terminal window and enter the following command:
nano ~/.bash_profile
or
nano ~/.zprofile
This will open the ~/.bash_profile or ~/.zprofile file in the Nano text editor.
- Add the following line to the file:
export PATH=~/Library/Android/sdk/tools:$PATH
export PATH=~/Library/Android/sdk/platform-tools:$PATH
Press Ctrl+X
to exit the Nano editor, then press Y
to save the changes and Enter
to confirm the filename.
- Run the following command to reload your shell configuration:
source ~/.bash_profile
or
source ~/.zprofile
After you have set the PATH for adb, you should be able to run the adb command from any terminal window.
By Manual:
- Go to the
Home
directory & tap command
+ shift
+ .
(on Mac system/laptop)

- Search file ~/.bash_profile or ~/.zprofile & open it.

- Add required path & save it.

export PATH=~/Library/Android/sdk/tools:$PATH
export PATH=~/Library/Android/sdk/platform-tools:$PATH
- Run the following command to reload your shell configuration:
source ~/.bash_profile
or
source ~/.zprofile
After you have set the PATH for adb, you should be able to run the adb command from any terminal window.