Go to the I-TASSER website (https://zhanglab.ccmb.med.umich.edu/I-TASSER/) and paste your protein’s FASTA sequence into the text box. The maximum number of amino acids that can be inputted in a single job is 1500. If necessary, you can split your FASTA sequence into multiple pieces and reconnect the models in YASARA, although this can be challenging. Hint: Use MobiDB tool (http://mobidb.bio.unipd.it) to identify the best location to split a FASTA sequence. You will need to register an email to receive your results from I-TASSER. Of note, if you attempt to build a homology model in YASARA and only receive a blank white screen it means that your desired protein shares no homology with any experimentally solved structures.
Also, you can try to find a predicted model on AlphaFold Protein Structure Database https://alphafold.ebi.ac.uk/. AlphaFold structures can be found by searching this database or on UniProt (https://www.uniprot.org/) by selecting AlphaFold as the Source in the Structure section of the protein entry.