Since you already have imported data from SQL server I'm asumming you are familiar with SQL queries, so for a more flexible approach you can execute INSERT statements using DBI::dbSendStatement(), take a look at this example.
rs <- dbSendStatement(
con,
"INSERT INTO cars (speed, dist) VALUES (?, ?)",
param = list(4L, 5L)
)
dbClearResult(rs)
Also, if you have multiple registers to insert and manually typing the sql statement would not be practical, you can use DBI::sqlAppendTable() to programmatically prepare the sql command.