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It should have reset once you filled the def reservoir.Since it has not reset this indicates the def fluid sensor may need recalibrated or there is an issue with one of the DEF tank components sending a false signal.
You may be able to drive it a short distance to see if it resets.If this was already done or is done and does not resolve the issue then you will need to have the def fault codes checked with a fully compatible scan tool or computer plugged into your vehicle that can read all computers to see what codes are set and then those codes diagnosed to locate and repair this fault here.
The dealer will need to recalibrate the level sensor as well in some cases.But you want to have this done soon before the start counts go to 0.
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