Below solutions may help to fix the issue.
Solution1
1. Update metro.config.js with following entry.
module.exports = {
transformer: {
assetPlugins: ['expo-asset/tools/hashAssetFiles'],
},
server: { port:8082, }
};
2. Open project.pbxproj file and replace the port no
3. react-native run-ios --port=<port num>
Solution2
1. Create a new react native project.
2. Open project.pbxproj
3. Change 8081 to different port
4. react-native run-ios --port=<port num>
5. If app is up and running then move your old project files to this new project.
Above solutions may resolve your problem.