If you have forgotten your 3CX Admin password there is no need to reinstall 3CX.
Create a 3CX Backup using the 3CX Backup and Restore Tool and save to your desktop.
This will output the backup to a compressed ZIP File
Unzip the backup file and open the contents.
Open the .XML file which is located on the main folder of the backup in Notepad
Use the Notepad find feature to look for WEBSERVERPASS
You should see contents like below
<Description>The admin pass</Description>
The parameter value contains the password and in this case the password was set to Thepassword