Maybe using something like this :
M=[-9999866 730537;
-999986 733865;
-9999747 731652;
-9999747 732028;
-9999747 729692;
-9999747 735361];
id=-9999747; % choose an id
indices where first row of M is equal to the desired id :
index=M(:,1)==id;
index =
6×1 logical array
0
0
1
1
1
1
And take the maximum of the corresponding serial number
max(M(index,2))
ans =
735361
