Conclusion

The purpose of correction is to restore, not condemn or humiliate, so that fellowship is restored. The person teaching the truths that correct any error must do so in love and humility while the person being shown the truths must be willing to accept the truths and the necessary changes that will be result from the implementation of these truths.
Before a person knows the errors they have in their belief system there is no sin attached to that belief, but once they know the truth then to continue in that erroneous belief is sin and to persevere in this sin may result in Loss of salvation (Rev 3: 5).
It should not need be said that any error to be corrected is one that The Bible calls error and not what man calls error
What must be done then if you see someone or a church/denomination doing something you do not do and which appears to be wrong.
Firstly, see if it passes the two tests.
If it does, then you cannot criticise it and may even benefit from its observance or understanding of it.  If it does not pass the two tests then you must correct in meekness as to a weaker brother/sister showing what The Bible says about the error less you sin in any way.
Perhaps you will gain your brother/sister and be able to fellowship with them.
Secondly, if they are shown the truth and will not correct the error then you cannot fellowship with them as they are in rebellion against God.  You are to leave them for God to deal with and get on with what Jesus wants you to do as they are His problem not yours.
What are you willing to give up to obey Jesus (The Bible) as that will determine how you relate to Him, obey Him and whether you have salvation or not.
Does it matter where you worship or who you worship with?
The Holy Spirit is in you so you can worship anywhere as for who you can worship with will be those you can fellowship with.  People who wholeheartedly follow Jesus as Lord and do not hold onto any errors that they know is in their belief system.
Epilogue
Many mistakes have been made in the past. The main one was to attack error using The Mosaic Law.  The Bible is our ruler to correct error but we cannot use parts of it that no longer apply as they have been made redundant by God’s Grace.  The Mosaic Law no longer applies in The New Testament so to use this to correct error is incorrect.
Jesus said that we are not to look at the past (Luke 9:62) but to the future or He can not use you for His purposes as He desires to use you.
Holding onto the past and living in unforgiveness can lose you your salvation and for that reason alone the past should be forgiven and forgotten and a new start made in the repentance and forgiveness that occurs in the unity of The Holy Spirit.
Jesus challenges you:

Do you desire to live truth?
What are you willing to give up to hold to or embrace truth?
What price Jesus?

On this may depend your eternal salvation.