First, the fpp2::uschange data is already a tsibble object in the fpp3 package, available as fpp3:us_change.
Second, you can convert any ts object to tsibble format using as_tsibble(). For example
library(fpp3)
as_tsibble(fpp2::uschange)
#> # A tsibble: 935 x 3 [1Q]
#> # Key: key [5]
#> index key value
#> <qtr> <chr> <dbl>
#> 1 1970 Q1 Consumption 0.616
#> 2 1970 Q2 Consumption 0.460
#> 3 1970 Q3 Consumption 0.877
#> 4 1970 Q4 Consumption -0.274
#> 5 1971 Q1 Consumption 1.90
#> 6 1971 Q2 Consumption 0.912
#> 7 1971 Q3 Consumption 0.795
#> 8 1971 Q4 Consumption 1.65
#> 9 1972 Q1 Consumption 1.31
#> 10 1972 Q2 Consumption 1.89
#> # … with 925 more rows
Created on 2022-06-07 by the reprex package (v2.0.1)