Seeking Assistance with Adding New Fields to Line Items – Requesting Community Support

My challenge revolves around adding new fields to the existing line items. Although I understand the importance of incorporating these fields to enhance our system’s functionality, I am currently unsure about the precise steps required to accomplish this task effectively.

I need to include the date & time filed into line items for my requirement. I have tried several methods but nothing has helped me.

please help me with the above.