Hi there, Iju Ahmed.
The option to sync the SKU and the UQC is unavailable. However, we can the SKU option and then add another custom field and then manually add the UQC.
Let me guide you how:
I've also added this reference for more information in customising the sales forms: Customise sales forms in QuickBooks Online.
I'm just a post-away if there's anything that I can help. Keep safe!