How could you explain that Hank Schrader did know about altercation between Mike Ehrmantraut and Tuco?

It's a lapse in the narrative.

Better Call Saul is the prequel to the series Breaking Bad. As such, it's narrative is supposed to align it with the events of the following series in a manner that precludes narrative lapses. However, for reasons of time and expense, as well as having different writers there have been several lapses in continuity, including this one.

Mike Ehrmentraut's run in with Tuco and the subsequent dealings with Tio Salamanca are never referenced in Breaking Bad. Since Mike was forced to retract his statement and risks arrest and prosecution for this, it seems to be more than a little odd that such a major event was not referenced in Breaking Bad. There were two chances to do (when Hank Schrader was pursuing Tuco and then later when the Fring organization collapsed and Mike was being questioned) and yet the producers and writers never avail themselves of the opportunity to do so. That's what makes it a narrative lapse.

While the series may attempt to cover this lapse with a scene or scenes which reference this oversight, there seems to be very little that can be done to correct. Just like Jimmy (Saul) having an older brother whose was an important attorney in ABQ,just like Jimmy relationship with Roz and just like Mike's granddaughter being the same age as in Breaking Bad whose events occur six years later, there are a number of lapses that have been made trying overlay the sequel with the prequel.