Best place to get that is to look at your statement if you are getting one. If not, contact that employer and ask for the HR department or the person responsible as the plans contact and they can direct you on how to find out your balances.
If you do not have a statement from the 401k custodian, you can contact the company that you work (or worked) for to get the contact information. If you are still working for that company, you may not be able to withdraw funds from your 401k, though there are often loan options available.
If you are no longer working for that company, you will want to understand the tax consequences of withdrawing funds from the account. I recommend speaking with a financial or tax advisor to guide you.
If you’re still employed with the company I would first check with HR and make sure they have a loan prevision on the Plan. If that’s the case most plans let you take 50% up to $50,000. You will have to pay that back on a set interest rate. It’s like taking a loan from yourself. If it for a first time home purchase they tend to let you us up to $10,000 with no penalty