Millie – if your proposed renovations really don’t involve any areas of common property such as the floor or perimeter walls adjoining other lots, then all you need do is to formally advise your Owners Corporation of that, of the date when works will commence, of the proposed hours of work, of when you expect completion, and to seek advice on any requirements it may wish to provide to you (within a timeframe) regarding contractors’ access to / across the common property.
If however as your post mentions “retiling of walls, floor and shower tray” is proposed as part of your works, and as that does involve the common property, then perhaps additionally ask your Owners Corporation if the same consent as was granted to the Chairman can apply to you?