You're going to have to get it fixed or replaced. Your lamp iris is broken. Quite a lot of us have had this. If you provide more details I can add you to the below list for morbid curiosity sake.
Indeed, I will do it for him

Current list below.
For what it is worth the more I use even my new, working unit, the more I think the iris drive logic is broken in several ways.
I've noticed a couple of times when switching to my first HDR title after power on the iris makes a quick "false move" - like it hits the end stop and comes back.
I believe (need to do some experiments) that if the unit powers off with the iris in HDR mode (at say iris 0) and then powers back on with SDR input (which would usually correspond to iris -9 for me) it doesn't always (maybe ever) move the lamp iris back to the correct -9 location for the corresponding SDR mode - it is like the projector doesn't know where the iris actually is. I think what then happens is you try to play HDR and it thinks it needs to drive the iris mech further to 0 (but it is already at 0!) and bounces off the end stop. The subsequent iris changes work fine.
Current list of users with failed irises:
@
bobof
UK, X7900, Fail 22/Jul/2018 @ 95hrs, Manuf 04/2018, SN 09340455, REPLACED
https://www.avsforum.com/forum/24-di...l#post56524896
@
TKNice
US, ?, Fail ?? @ a few hundred hrs, Manuf ?, SN ?, REPLACED
https://www.avsforum.com/forum/24-di...l#post56499926
@
br0d0
Australia, X7900, Fail 14/Jul/2018 @ 52hrs, Manuf 01/2018, SN 06340278, REPAIRED
https://www.avsforum.com/forum/24-di...l#post56488090
@
coxy2416
Canada, X790, Fail 20/May/2018 @ 20hrs, Manuf 04/2018, SN 09340399, REPLACED
https://www.avsforum.com/forum/24-di...l#post56525152
@
JJ7
USA, RS540, Fail 29/Dec/2017 @ 20hrs, Manuf Nov 2017, SN 162402xx, REPLACED
https://www.avsforum.com/forum/24-di...l#post55396160
@
ScottAvery
US, RS540, Fail 25/Jul/2018 @ 134hrs, Manuf ?, SN ?,
failure hasn't stuck hard like most
https://www.avsforum.com/forum/24-di...l#post56540012
@
BdoUK
, USA, RS540, Fail 21/Sept/2018 @ 350hrs, Manuf 01/2018, SN 06340302, Still with user,
https://www.avsforum.com/forum/24-di...l#post56847266
@
jackshi
, ?, RS540, Fail @ 1week old, Manuf?, SN?, REPLACED,
https://www.avsforum.com/forum/24-di...l#post56847666
@
jwhart
, USA, X990, hrs?, Manuf?, SN?, Outcome?,
https://www.avsforum.com/forum/24-di...l#post57200020
@
rlarsen462
, USA, X990, hrs?, Manuf?, SN?, Outcome?,
https://www.avsforum.com/forum/24-di...l#post57257192