Not shifting

Hi Ken, nice to meet you,

thank you for your answer, but shooting for this problem is not possible easily cause I don't know when would it occur when I'm driving and it comes and backs alternatively, but I have my old disk and it's obviously ruined without prominence that they must have been on the plate and they are not. So it obviously needed to get changed by causing a firm clutch. Now my clutch is super soft and convenient and I have no problem with my clutch but I have huge problem with gear number 1 that is just sometimes as I said before in those situations.
Now I'm looking for the main reason that our mechanics can not figure it out. Whenever they test it, gear number 1 is okay and it needs driving more up to a point that gear number 1 doesn't shift in its place and I have to go to gear number 2 then move a little then bring it back to number 1 which is meaning when the car is moving as I said before.
But about air presence in clutch disk I've never heard and I'm gonna follow it.
And now any opinion that you have it's so appreciated, I'm waiting.
Sincerely

Could you please explain more about this sentence ""(Also does it feel like air is in the clutch master?)""
By the way, if I can get a video from this situation I will send you asap.
Thanks in advance.
Regards

Actually it feels a little a kind of what you said, but as I said before my clutch pedal is super soft, and one more thing that I have to say to you : someone told me when the gear 1 is not going to shift, I should leave clutch pedal and then I press it down again, after that I go through gear 1 and I did test it and it did respond good and gear 1 did not bother however it's abnormal.
It means I have to press pedal twice when the gear 1 is bothering me then it will be okay.

Now what do you think?
In fact about the video, I don't know exactly what kind of video I have to share. I hope you can help me just by my explanations.

Thanks a lot Ken.

I studied a little bit about clutch master right now, and I think you are right 99% and the issue is coming from it.
But the problem is that I don't know which part of car is called (clutch master cylinder).
Now if you could give me please a really simple explanation about it so that I can understand easily what is (clutch master) in my car then I tell to my mechanic. In my idea this unsolvable problem will get solved.

By the way sincerely thanks because of your consistency.

Excuse me Ken for being late in reply, actually I was figuring it out during this time but I couldn't. My car has not clutch master or a pump for clutch, actually it uses a clutch wire instead of.
Now what can possible go wrong with my gear 1?

About clutch disk I DID say to you I used a best one of disk original valeo if you have a look at previous chats, about gears YES they did but first, all other gears are okay.
Now excuse me I wanna know what does "transmission syncro" mean?
Do you mean gear box?
What do you mean by "rebuild"?