Model Protein Structure greater than 1500 amino acids

Dear I-TASSER team,

I have target protein sequence with >4000 amino acid in length that i
wanna model. since I-TASSER server cannot model more than 1500 amino
acids, so i split my protein sequence into three parts and separately
model the each part by I-TASSER server. can you please suggest is
there any way to combine the modelled protein back into full protein
or is there any way to model the complete protein with more than 4000
amino acids?

I hesitate to use I-TASSER standalone because i don't have personal computational resources, and because i am new in protein modeling so don't know the file formats as well. Can you please guide me step-by-step to solve my issue.

I will wait for your kind response anxiously..

Thanks!

Kind Regards
sohail