Is there any problem in garmmar

Problems:
(1) Grammar
(2) Sentence structure is too long
(3) Typical HK-style English

My suggestion:
The modification work of the training room will be carried out in early September. Hence, ML room has been reserved for you instead.

Notes:
If you want to use your own sentence, the term "will be shifted" is incorrect. Since you have already known that the training room will not be available in early September, your reservation "has been shifted" but NOT "will be shifted" to ML room instead. You must use Present Perfect Tense in this case. If you use Future Tense, it means that the reservation will be shifted for you later but not at that moment.

Since modification work to the Training Room will be carried out in early September, your reservation for the Training Room will be changed to ML Room instead.

As Training Rm has modification work which will be carried in early September
( the above statement is a fragment)
Revised below:
The modification work of the training room will be carried in early September. Hence, your original room reservation will be shifted to ML Room instead