First of all, this is not recommended. Make sure your PC is secured, and no one has access to it. Then you can try the following:
Run REGEDIT
Find
HKEY_CURRENT_USER\Software\SAP\
HKEY_CURRENT_USER\Software\SAP\
--> Right Click on SAP
--> Then New
--> Key with name SAPShortcut
--> Then using Same above Step create a key name "Security" under "SAPShortcut"
--> Now Right Click on the Security --> New --> String Value
--> Give Name "EnablePassword" to this and Set it Value 1
Then Close regedit and if SAP GUI open close it too
Now open SAP GUI and you will find the Password Field Enable.
--> Then New
--> Key with name SAPShortcut
--> Then using Same above Step create a key name "Security" under "SAPShortcut"
--> Now Right Click on the Security --> New --> String Value
--> Give Name "EnablePassword" to this and Set it Value 1
Then Close regedit and if SAP GUI open close it too
Now open SAP GUI and you will find the Password Field Enable.