How to use placeholder in knex set query

I am trying to use placeholder in knex set query. But I am getting the same error for all the cases. How to do this properly?

await db.raw('set timezone = $1', { timezone });
await db.raw('set timezone = :timezone', { timezone });
await db.raw('set timezone = ?', [timezone]);

error:

set timezone = $1 - syntax error at or near "$1"

The timezone is coming from http query. I need it to get aggregated data based on date at client’s timezone. In database (postgresql), the date is saved in column with type timestamp with timezone. The timezone the data is saved is in UTC time.