ClearAll["Global`*"]
Symbs={
{"(Subscript[U, 1])","USubscript1"},
{"(Subscript[U, 2])","USubscript2"},
{"(Subscript[U, 3])","USubscript3"},
{"(Subscript[(OverVector[U]), n])","OverVecUSubscriptn"},
{"(Subscript[(OverVector[X]), r])","OverVecXSubscriptr"},
{"(OverVector[U])","OverVecU"},
{"(OverVector[X])","OverVecX"},
{"(OverVector[χ])","OverVecChi"},
{"(Subscript[X, 1])","XSubscript1"},
{"(Subscript[X, 2])","XSubscript2"},
{"(Subscript[X, 3])","XSubscript3"},
{"(Subscript[𝒳, 1·])","χSubscript1"},
{"(Subscript[𝒳, 2·])","χSubscript2"},
{"(Subscript[𝒳, 3·])","χSubscript3"},
{"(Subscript[χ, 1·])","χ[[1]]"},
{"(Subscript[χ, 2·])","χ[[2]]"},
{"(Subscript[χ, 3·])","χ[[3]]"},
{"(Subscript[n, 1])","nSubscript1"},
{"(Subscript[n, 2])","nSubscript2"},
{"(Subscript[n, 3])","nSubscript3"},
{"(Subscript[Un, 1])","UnSubscript1"},
{"(Subscript[Un, 2])","UnSubscript2"},
{"(Subscript[Un, 3])","unSubscript3"},
{"(Subscript[Γ, (Subscript[g, 1])])","ΓSubscriptg1"},
{"(Subscript[Γ, (Subscript[g, 2])])","ΓSubscriptg2"},
{"(Subscript[Γ, (Subscript[g, 3])])","ΓSubscriptg3"},
{"(Subscript[Γ, (Subscript[g, 4])])","ΓSubscriptg4"},
{"◦","@@"}
};

ClearAll[CreateComps];
CreateComps[comps_List,NoRepeat_]:=Module[{SymbComp1={},SymbComp2={},SymbComp3={},SymbComp4={},SymbComp},


Do[
AppendTo[SymbComp1,{i<>"·",StringJoin["[[",i,"]]"]}],
{i,comps}
];


Do[
If[
If[NoRepeat,i≠j ,True],
AppendTo[SymbComp2,{i<>"·"<>j<>"·",StringJoin["[[",i,",",j,"]]"]}]],
{i,comps},{j,comps}
];

Do[
If[
i≠j && j≠ k ,
AppendTo[SymbComp3,{i<>"·"<>j<>"·"<>k<>"·",StringJoin["[[",i,",",j,",",k,"]]"]}]],
{i,comps},{j,comps},{k,comps}
];


Do[
If[
i≠j && j≠ k && k≠ l,
AppendTo[SymbComp4,{i<>"·"<>j<>"·"<>k<>"·"<>l<>"·",StringJoin["[[",i,",",j,",",k,",",l,"]]"]}]],
{i,comps},{j,comps},{k,comps},{l,comps}
];

SymbComp=Join[SymbComp4,SymbComp3,SymbComp2,SymbComp1];
Return[SymbComp];
]

ClearAll[SymbComp,NumberComps];
SymbComp=Join[CreateComps[{"i","j","k","l"},True],CreateComps[{"1","2","3"},False]];

nb=NotebookOpen["/Users/hkesari/Downloads/LinearElasticityPlainStrainStressStrain_dummy.nb"]

For[i=1,i≤ Length[Symbs],i++,
KeepSearching=True;
OldName=Symbs[[i,1]];
NewName=Symbs[[i,2]];
(*Print[i," ",OldName," ",NewName];*)
If[ NotebookFind[nb,OldName,WrapAround->True]==$Failed, KeepSearching=False,KeepSearching=True];
While[KeepSearching,
NotebookApply[nb,NewName];
If[ NotebookFind[nb,OldName,WrapAround->True]==$Failed, KeepSearching=False,KeepSearching=True]];
]

nb=NotebookOpen["/Users/hkesari/Downloads/LinearElasticityPlainStrainStressStrain_dummy.nb"];
For[i=1,i≤ Length[SymbComp],i++,
KeepSearching=True;
OldName=SymbComp[[i,1]];
NewName=SymbComp[[i,2]];
(*Print[i," ",OldName," ",NewName];*)
If[ NotebookFind[nb,OldName,WrapAround->True]==$Failed, KeepSearching=False,KeepSearching=True];
While[KeepSearching,
NotebookDelete[nb];
NotebookDelete[nb];
NotebookApply[nb,NewName];
If[ NotebookFind[nb,OldName,WrapAround->True]==$Failed, KeepSearching=False,KeepSearching=True]];
]