Thank you all for the answers. Vilas, that is how I have been doing it. However the doubt arises when checking that extrapolation is only mentioned on MTOW section and not with FLEX TEMP method. in addition to not being able to proceed as per STEP number 1 that says: "Interpolate for actual takeoff weight. Read flexible temperature associated with this weight." that weight is not on the chart, so we can't really "interpolate".
I know the easiest way is to read the highest FLEX TEMP and use those speeds assuming a heavier weight.