How to remove this concave?

Answer 1

[KALYAN ACHARJYA]

% You can change the thresholds values as per your requirements/More accurate
BW=im2bw(rgb2gray(imread('bin1.png')));% You provided the RGB Image
BW1=bwmorph(BW,'thicken',20);
BW2=bwmorph(BW1,'majority',50);
figure,

 imshow(BW2);

[KALYAN ACHARJYA]

Or do the sorts of morphological operations, you will get the result

[attawut kovitvadhi]

I am very appreciated for this answer. Thank you a lot.

[KALYAN ACHARJYA]

My Pleasure @Attawut