Hi Jagroop,
There is no "simple" way to convert Trusted Launch VM to Standard VM. If you don't have a lot of customizations/data in your VM I recommend creating a new VM with Security type: Standard, manually copying over any data from original VM, and re-perform any customizations inside of the VM.
If it would take many hours to manually re-do all the work to a new VM as described above, there is a multi-step process I have used in the past. Before doing it I recommend shutting down the VM and taking snapshot.
Basic steps are Export the disk (generate SAS), use azcopy to copy it to blob in storage account, create new disk from blob, create new Standard VM, shut down VM, swap OS disk with new disk created above, start VM and check that everything is okay.
Please click Accept Answer and upvote if the above was useful. If you decide to perform the more complicated export procedure above and need more details on a specific step let me know and I can assist.
Thanks.
-TP