Converting numeric column to week number in r

Question

I am trying to create a seasonal plot with this data however my week numbers are just values and not actual dates.

view(Demandts)

# A tsibble: 255 x 2 [1]
# Key:       Week [255]
    Week Demand
   <dbl>  <dbl>
 1     1     48
 2     2    101
 3     3    129
 4     4    113
 5     5    116
 6     6    123
 7     7    137
 8     8    136
 9     9    151
10    10     87
# ... with 245 more rows

I have created a time series plot with the current tsibble:

How would I turn my first column into dates or periods so that I can find seasonality?