I have a CRS326-24S+2Q+R and I want to test a 100GB transceiver (in a 40Gb port), to do this the provider asks me to tun off CDR thru the equipment, but I could not find a way to do this, anyone that can help me with this?
Do you perhaps mean CDP?
This is done under ip neighbors
This one’s a bit tricky. CDR btw is Clock Data Reconstruction/Recovery, that is, the QSFP / QSFP28 module includes a suitable PLL that synchronizes on clock embedded in the data stream and helps clear up the eye diagram.
The problem is basically this: The CDR circuit included in the modules functions in a rather narrow (roughly +/- 5-10%) region around the nominal clock (28G for QSFP28 and 10.3G for QSFP). This means that a) with CDR enabled the bit error rate will be terrible, probably you are lucky to get any data at all b) with CDR disabled you will still get worse than specified performance c) in both cases LOS (Loss of Synchronization) error will occur.
So the short answer is: if you want this to work correctly, use QSFP modules. These have the correct CDR circuitry and will provide good performance. (The equipment on the other side of the link supports them for sure - most serdes chips do - otherwise they wouldn’t be able to use the QSFP28 in 40Gbps mode.)
The longer answer is that Mikrotik supports ignoring the LOS signal. As far as I can tell it does not support disabling CDR. (While any feature that enables some compatibility is welcome in my book, it’s generally not a good idea to disable it.) But if you would like support for it - write to support 
Mikrotik may do it silently if it detects such a mismatch… If you want to look, you can find it in the eeprom readout at address 98 (0x62), the high nibble being CDR for xmit 4..1, the lower nibble CDR for rcvd 4..1. (1=enabled 0=disabled) Many/most modules support this readout.