Hi, ratnakar vibhute
You can get the MFGTool for i.MX8mq from this link.
To flash multiple devices at the same time using MFGTool, you need to modify UICfg.ini file.
In this file, PortMgrDlg variable indicates how many boards can be supported simultaneously. By default PortMgrDlg=1, but it can support up to four boards.
So, PortMgrDlg can be set to 1-4.