avova() returns a table object. You need to access its value like any normal table: https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html
For example, consider this code from the documentation page of avova:
load hospital
tbl = table(hospital.Age,hospital.Sex,hospital.BloodPressure(:,2), ...
'VariableNames',{'Age','Sex','BloodPressure'});
tbl.Sex = categorical(tbl.Sex);
mdl = fitlm(tbl,'BloodPressure ~ Sex + Age^2')
tbl = anova(mdl)
Result
>> tbl
tbl =
4×5 table
SumSq DF MeanSq F pValue
______ __ ______ _______ ________
Age 18.705 1 18.705 0.40055 0.52831
Sex 222.09 1 222.09 4.7558 0.031643
Age^2 30.934 1 30.934 0.66242 0.41772
Error 4483.1 96 46.699
You can access values like this
>> tbl.pValue(4)
ans =
0.5000
>> tbl{1,1}
ans =
18.7052
>> tbl{3,2}
ans =
1
>> tbl{2,5}
ans =
0.0316
or
>> tbl.SumSq(1)
ans =
18.7052
>> tbl.DF(3)
ans =
1
>> tbl.pValue(2)
ans =
0.0316
