To set up Currency Rates in Magento 2 take the following steps:
1. Go to Admin Panel > Stores > Currency Rates. 

  • This section enables you to configure the multi-currencies rates manually.
  • Otherwise, you can manage to set them up in Import Service choosing the service you want the rates to be automatically imported from.

Magento 2 Currency Rates,Import Service

 2. Save changes pressing Save Currency Rates button and then flush Magento cache.

Magento2 Save Currency Rates