Even partners have to pay for that.
A cheaper option is to buy these:
https://smile.amazon.com/Introduction-Fortigate-Part-I-Infrastructure-Fortinet-ebook/dp/B08B7N7P2X/ref=sr\_1\_3?crid=31D7PJYPITFKE&dchild=1&keywords=nse4+study+guide&qid=1625071918&sprefix=nse4+%2Clawngarden%2C169&sr=8-3
and
https://smile.amazon.com/Introduction-FortiGate-Part-II-Infrastructure-Fortinet-ebook/dp/B08GTMQ62F/ref=sr\_1\_4?crid=31D7PJYPITFKE&dchild=1&keywords=nse4+study+guide&qid=1625071918&sprefix=nse4+%2Clawngarden%2C169&sr=8-4
https://www.amazon.ca/gp/product/B08B7N7P2X/ref=dbs_a_def_rwt_hsch_vapi_taft_p1_i1
A good friend wrote this - he works for Fortinet. Pretty solid training guide.