Thank you for using Syncfusion products.
We have prepared the sample to illustrate your requirement to repeat the header row for each instance of the mail merge data record. Please do find the sample from the attachment. Try running the sample and let us know if this meets your requirement.
If the given sample doesn’t meets your requirement , please provide us the sample along with the input template document which you have used to generate the word document on your side, so that we can further analyze and update you with the appropriate details.
Please let us know if you have questions.