SSIS Find & Reverse Function

I am trying to get the date from the below filename using ssis expression.i get this file name from the variable

I have tried using findstring and reverse function but it still throwing cannot parse.

Any recommendtions pls

Variable

@[User::CurrentFile] : Z:\RETAIL DATA\HN_NLG\Supplier_report_by_Brand_Trend Micro_WC_20170327.xlsx

Need to get 20170327 and convert to 2017-03-27

Thanks in advance