The HSA belongs to you so you should have the paperwork. Note that your employer may have helped you set the HSA up, but it is still yours, not your employer's. This is similar to an IRA.
Since the employer might have helped you set it up and since it is likely that your employer is sending HSA contributions to the HSA custodian, you should be able to contact your HR department and ask them who the HSA custodian is.
Once you have identified yourself to the HSA custodian, you should be able to get your history. Note that most HSA custodians will offer online access to an HSA account, so ask the HSA custodian to help you set that up.
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