It should just do it automatically, but you can use DiskGenius to analyse and re-allocate sectors. Very good simple analysis tool for SSDs.

 

A building where SSDs are made.

 

Open a command prompt and type this in exactly where "C" below after -DriveLetter is the drive letter of your external drive


Optimize-Volume -DriveLetter C -ReTrim -Verbose


There are a few dedicated pieces of software that can defrag an SSD properly and safely like SSD Optimizer by Auslogics as one but it does not defrag in the true sense rather than trim and relocate files.

 

You can also use the software to copy your old hard drive, for example, the HDD C:/, along with the operating system, to the new SSD using the migration tool. I've enabled Rapid and Overprovisioning under "Performance."

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1.) TRIM ia a command not supported via USB. If Windows "Defragment and Optimize" detects your enclosure as SSD, you can use its OPTIMIZE function or resort to third-party software to force-trim manually or on schedule.
Another option is to make a batch file with "defrag X: /L /U /V" (X is the letter of your SSD) and use it manually, or set up a schedule in Windows Scheduler.

To create a .bat file, paste the defrag X: /L /U /V command into Notepad, hit 'File'->'Save As" and save it as trim.bat
You can then use this file manually or set up on a schedule.

2.) On my systems, Windows 11 recognizes one USB SSD as an SSD and will perform the Trim function on it but will not perform the Trim function on a second USB connected SSD drive. Attempting to execute defrag X: /L /U /V returns an error that the function is not compatible with the drive.

Source: https://learn.microsoft.com/en-us/answers/questions/811176/trim-on-external-usb-ssd