The first thing you’ll need to do is obtain the details of your new 401(k) plan.
The human resources department should be able to tell you the account address. (It’s also worth asking them about the fund’s performance and cost so that you can compare it to your previous employer’s 401(k) plan.)
You’ll then need to get back in touch with the human resources department at your previous employer and inform them of the details of your new 401(k) plan. They’ll either send the money directly to your new 401(k) plan or mail you a check made out to the plan.