How to use digital signature dongle for filing ...

I am using I Pad Pro 12.9" 128 GB wifi+cellular.

I am a Tax Consultant.

I am not able to use digital signature dongle to verify the tax return prepared on I Pad Pro and to file/upload the return. Can you guide me to solve this problem Please ? Is there any assessory through which the pen drive containg digital signature data can be attached with I Pad pro?