Please see the FAQ: What's a reproducible example (`reprex`) and how do I do one? Using a reprex, complete with representative data will attract quicker and more answers. In this case, it's almost complete, but without digging, it's hard to know what package to look for as.yearqtr in.
Here's an alternative
library(lubridate)
#>
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#>
#> date, intersect, setdiff, union
x <- ymd(c("2012-03-26", "2012-05-04", "2012-09-23", "2012-12-31"))
quarter(x, with_year = TRUE, fiscal_start = 11)
#> [1] 2012.2 2012.3 2012.4 2013.1
Created on 2020-04-08 by the reprex package (v0.3.0)